This thesis details my examination of several mechanisms for modulation of N-type calcium channels in neonatal rat superior cervical ganglion (SCG) neurons. The first part of this work characterizes cross-talk between two distinct mechanisms of modulation: readily-reversible inhibition induced by activation of heterotrimeric G-proteins (termed G-protein-mediated inhibition), and phosphorylation of the channel by protein kinase C (PKC). Data previously presented by other groups suggested that one effect of activating PKC is to prevent G-protein-mediated inhibition. The goal of this project was to confirm this hypothesis by testing functional competition between these two pathways. My findings show that G-protein-mediated inhibition blocks the effects of activating PKC, and that phosphorylation by PKC blocks G-protein-mediated inhibition, confirming that these two mechanisms are mutually exclusive. In addition, I investigated the effect of activating PKC on whole-cell barium currents in the absence of G-protein-mediated inhibition. When endogenous G-proteins were inactivated by dialyzing the cell with GDP-β-S, a guanine nucleotide that prevents activation of the G-protein's α subunit, activation of PKC with phorbol esters was without obvious effect on whole-cell current amplitude, fast and holding potential-dependent inactivation, and voltage-dependent activation, suggesting that PKC's principal role in modulating these currents is to prevent G-protein-mediated inhibition. From these results, I advanced Bean's 1989 model of reluctant and willing gating (induced by G-protein-mediated inhibition and relief of that inhibition, respectively). In this expanded model, reluctant channels, inhibited by G-proteins, are resistant to phosphylation by PKC (reluctant/P-resistant). Unmodulated channels are called willing/available, as they exhibit willing gating, and are available for either binding to a G-protein or phosphorylation by PKC. Finally, phosphorylation of a willing/available channel by PKC drives the channel into the willing/G-resistant state, in which the channel gates willingly, and is resistant to G-protein-mediated inhibition. These results are published in the Journal of General Physiology(2000; 115:277-286), and are presented in this thesis as Chapter II. In addition to membrane-delimited inhibition, N-type calcium channels are also subject to inhibition via a diffusible second-messenger pathway. In SCG neurons, this inhibition can be observed following stimulation of M1 muscarinic receptors by the agonist oxotremorine-M. Our lab previously hypothesized that the diffusible messenger involved might be the polyunsaturated fatty acid arachidonic acid (AA). To test this hypothesis, our lab examined the effect of bath-applied AA on whole-cell SCG calcium currents, and demonstrated that AA induces inhibition with similar properties as M1 muscarinic inhibition. An analysis of AA's effects on unitary N-type calcium currents, published by Liu and Rittenhouse in Journal of Physiology(2000; 525:391-404), revealed that this inhibition is mediated, at least in part, by both a significant increase in the occurrence of null-activity sweeps and a significant decrease in mean closed dwell time. Based on these results, our lab conducted an examination of AA's effects on whole-cell currents in SCG neurons, and found that AA-induced inhibition is mediated by an increase in holding potential-dependent inactivation and appears independent of AA metabolism. When I examined AA's effects in greater detail, I discovered that, in addition to inhibition, AA also appeared to cause significant enhancement of whole-cell currents. The results characterizing AA's general effects on whole-cell calcium currents in SCG neurons have been published in American Journal of Physiology - Cell Physiology(2001; 280:C1293-C1305). Because my finding that AA enhances whole-cell neuronal calcium currents revealed a novel pathway through which this current can be modulated, I proceeded to characterize this effect. My results showed that enhancement develops significantly faster than inhibition, suggesting different mechanisms or pathways. In addition, dialyzing the cell with BSA, a protein that binds fatty acids, blocked the majority of AA-induced inhibition, but did not reduce enhancement, suggesting that enhancement is independent of inhibition and might be mediated at an extracellular site. Using fatty acid analogs that cannot cross the cell membrane, I confirmed that enhancement occurs extracellularly. My data also indicate that AA-induced enhancement of whole-cell currents does not require metabolism of AA, consistent with enhancement being mediated directly by AA. I also examined the biophysical characteristics of enhancement, and found that both an increase in the voltage sensitivity of activation and an increase in activation kinetics underlie this effect. Finally, using both pharmacological agents and a recombinant cell line, I presented the first demonstration that AA enhances N-type calcium current. These findings are described in detail in a paper recently published in American Journal of Physiology - Cell Physiology(2001; 280:C1306-C1318), and are presented in this thesis as Chapter III. In our investigation of AA's effects on whole-cell calcium currents, we utilized a voltage protocol, in conjunction with pharmacology, to enhance the level of L-type current in these cells. Since whole-cell calcium currents in SCG neurons are comprised of mostly (80-85%) N-type current, with the remaining current comprised of mostly L-type current, this approach allowed us to examine both N- and L-type currents. When currents are recorded in the presence of 1 μM FPL 64174 (FPL), a benzoyl pyrrole L-type calcium channel agonist first described in 1989, stepping the membrane potential to -40 mV following a test pulse to +10 mV generates a slowly-deactivating ("tail") current. This tail current is made up entirely of L-type current, and allows us to readily investigate the effect of various modulatory mechanisms on this current type. Although FPL has been used for almost a decade to study L-type calcium currents, activity of FPL on N-type calcium currents has not been investigated. Because our lab routinely uses micromolar concentrations of FPL to measure whole-cell and unitary calcium currents in neuronal cells, I tested whether FPL has any effects on N-type calcium current. Therefore, I examined the effect of FPL on whole-cell calcium currents in an HEK 293 cell line that expresses recombinant N-type calcium channels. Application of 1 and 10 μM FPL caused significant, voltage-independent inhibition of currents, demonstrating that FPL inhibits N-type calcium current. Thus, at micromolar concentrations, FPL is not selective for L-type calcium current, and any examination of its effects on whole-cell calcium currents should take this into account. The results describing FPL's effects on L- and N-type calcium currents are included in a manuscript currently in preparation, and are presented as Chapter IV.

Myosin II and actin are two major components of the ingressing cortex during cytokinesis. However, their structural dynamics and functions during cytokinesis are still poorly understood. To study the role of myosin II in cortical actin turnover, dividing normal rat kidney (NRK) cells were treated with blebbistatin, a potent inhibitor of the non-muscle myosin II ATPase. Blebbistatin caused a strong inhibition of actin filament turnover and cytokinesis. Local release of blebbistatin at the equator caused inhibition of cytokinesis, while treatment in the polar region also caused a high frequency of abnormal cytokinesis, suggesting that myosin II may play a global role. These observations indicate that myosin II ATPase is essential for actin turnover and remodeling during cytokinesis. To further study the mechanism of myosin II and actin recruitment to the cytokinetic furrow, equatorial cortex were observed with total internal reflection fluorescence microscope (TIRF-M) coupled with spatial temporal image correlation spectroscopy (STICS) and a new approach termed temporal differential microscopy (TDM). The results indicated at least partially independent mechanisms for the early equatorial recruitment of myosin II and actin filaments. Cortical myosin II showed no detectable directional flow toward the equator. In addition to de novo equatorial assembly, localized inhibition of disassembly appeared to contribute to the formation of the equatorial myosin II band. In contrast, actin filaments underwent a striking, myosin II dependent flux toward the equator. However, myosin II was not required for equatorial actin concentration, suggesting that there was a flux-independent, de novo mechanism. The study was then extended to retraction fibers found typically on mitotic adherent cells, to address the hypothesis that they may facilitate post-mitotic spreading. Cells with retraction fibers showed increased spreading speed in post-mitotic spreading compared to cells without retraction fibers. In addition, micromanipulation study suggested that retraction fibers may guide the direction of post-mitotic spreading. Focal adhesion proteins were present at the tips of retraction fibers, and may act as small nucleators for focal adhesions reassembly that help cell quickly respread and regrow focal adhesions. These findings may suggest a general mechanism utilized by adherent cells to facilitate post-mitotic spreading and reoccupy their previous territory.

Thesis (Ph. D.)--Uniformed Services University of the Health Sciences, 2005. / Typescript (photocopy).

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2008. / Härtill 6 uppsatser.

Hepatocellular carcinoma (HCC) is a common malignancy of the liver that is one of the most frequent causes of cancer-related death in the world. Surgical resection and liver transplantation are the only curative options for HCC, and tumor invasion and metastasis render many patients ineligible for these treatments. Identification of the mechanisms that contribute to invasive and metastatic disease may enlighten therapeutic strategies for those not eligible for surgical treatments. In this dissertation, I describe two sets of experiments to elucidate mechanisms underlying HCC dissemination, involving the activities of Krüppel-like factor 6 and a particular p53 point mutation, R172H. Gene expression profiling of migratory HCC subpopulations demonstrated reduced expression of Krüppel-like factor 6 (KLF6) in invasive HCC cells. Knockdown of KLF6 in HCC cells increased cell transformation and migration. Single-copy deletion of Klf6 in a HCC mouse model results in increased tumor formation, increased metastasis to the lungs, and decreased survival, indicating that KLF6 suppresses both tumor formation and metastasis in HCC. To elucidate the mechanism of KLF6-mediated tumor and metastasis suppression, we performed gene expression profiling and ChIP-sequencing to identify direct transcriptional targets of KLF6 in HCC cells. This analysis revealed novel transcriptional targets of KLF6 in HCC including CDC42EP3 and VAV3, both of which are positive regulators of Rho family GTPases. Concordantly, KLF6 knockdown cells demonstrate increased activity of the Rho family GTPases RAC1 and CDC42, and RAC1 is required for migration induced following KLF6 knockdown. Moreover, VAV3 and CDC42EP3 are also required for enhanced cell migration in HCC cells with KLF6 knockdown. Together, this work describes a novel signaling axis through which KLF6-mediated repression of VAV3 and CDC42EP3 inhibits RAC1Gmediated HCC cell migration in culture, and potentially HCC metastasis in vivo. TP53 gene mutations are commonly found in HCC and are associated with poor prognosis. Prior studies have suggested that p53 mutants can display gain-of- function properties in other tumor types. Therefore, I sought to determine if a particular hotspot p53 mutation, p53R172H, provided enhanced, gain-of-function properties compared to p53 loss in HCC. In vitro, soft agar colony formation and cell migration is reduced upon knockdown of p53R172H, indicating that this mutation is required for transformation-associated phenotypes in these cells. However, p53R172H-expressing mice did not have enhanced tumor formation or metastasis compared to p53-null mice. These data suggest that p53R172H and p53 deletion are functionally equivalent in vivo, and that p53R172H is not a gain-of-function mutant in HCC. Inhibition of the related transcription factors p63 and p73 has been suggested as a potential mechanism by which mutant p53 exerts its gain-of-function effects. Analysis of p63 and p73 target genes demonstrated that they are similarly suppressed in p53-null and p53R172H-expressing HCC cell lines, suggesting a potential explanation for the phenotypes I observed in vivo and in vitro. Together, the studies described in this dissertation increase our understanding of the mechanisms underlying HCC progression and metastasis. Specifically, we find and characterize KLF6 as a novel suppressor of HCC metastasis, and determine the contribution of a common p53 point mutation in HCC. This work contributes to ongoing efforts to improve treatment options for HCC patients.

Vesicle budding, membrane trafficking, and lipid metabolism depend on the switching of Arf and Rab GTPases from the inactive GDP bound state to the active GTP bound state. However, Arf and Rab GTPases have intrinsic rates of GDP to GTP exchange that are much slower (hours to days) than the time scale of the relevant trafficking processes (seconds or less). In cells, the activation of Arf and Rab GTPases is tightly regulated by guanine nucleotide exchange factors (GEFs) with Sec7 or Vps9 domains, respectively. Full length Cytohesins, which have a domain architecture consisting of heptad repeats, a Sec7 domain, a pleckstrin homology (PH) domain, and a polybasic motif, have 100-fold lower exchange activity than the isolated Sec7 domain. Insights into the low exchange activity were obtained by structural, biochemical and kinetic analyses. It was found that the Sec7-PH domain linker and a C-terminal amphipathic helix physically block the docking sites for the switch regions of Arf GTPases. Mutations within either element result in partial or complete relief of autoinhibition. Autohibition is also strongly relieved by phosphorylation of protein kinase C (PKC) sites in the polybasic motif of Cytohesin-1 or by phosphoinositide head group-dependent binding of active Arf6. Despite unrelated folds, Sec7 and Vps9 domains engage cognate GTPases in a strikingly similar manner and supply a critical acidic residue that interacts with an invariant lysine residues from phosphate binding (P) loop of the GTPase in the nucleotide free complex. The key acidic residues have also been proposed to disrupt the Mg2+ binding site; however, it is not known whether disruption of Mg2+ binding contributes to the rate limiting step for nucleotide release. To investigate the kinetic mechanism for catalysis of nucleotide exchange in the absence of autoinhibitory interactions, a detailed stopped flow kinetic analysis of the intrinsic and GEF mediated exchange reactions was conducted for the isolated catalytic cores. Using three different fluorescence methods to monitor Mg2+ dissociation, formation of the nucleotide free intermediate, and subsequent nucleotide binding, the catalytic cores of Cytohesin-1 and Rabex-5 were found to robustly accelerate nucleotide exchange on Arf1 and Rab5, respectively, by at least 105- fold at physiological concentrations of Mg2+. The acceleration of nucleotide exchange was reduced by roughly an order of magnitude at sub-micromolar concentrations of Mg2+. In addition, the Cytohesin-1 and Rabex-5 catalytic cores have similarly high catalytic efficiencies (kcat/KM) as well as high lower limits on both the rate (kcat) and steady state (KM) constants for GDP release at physiological as well as low Mg2+ concentration. The limits on kcat and KM are comparable to the highest values reported for other well characterized GEFs and likely reflect dual requirements of membrane targeting and autoregulatory mechanisms for tight control of catalytic output. These results provide a solid structural and mechanistic foundation for future experiments to investigate the spatial-temporal dynamics of Cytohesin and Rabex-5 activation in cellular contexts.

A migração de células musculares lisas (VSMC) da camada média do vaso para a íntima é essencial para vasculogênese e contribui para o processo de aterosclerose e estenose após lesão por cateter-balão, caracterizando-se como um importante alvo terapêutico. Diversos trabalhos já demonstraram que fatores de crescimento (como PDGF e FGF) estimulam a migração de VSMC, inclusive, muitos desses fatores de crescimento induzem sinalização redox associadas à geração de espécies reativas de oxigênio (ROS) (ex. Nox1 NADPH oxidase). Nosso grupo já descreveu interações físicas e regulação funcional da NADPH oxidase por uma chaperona redox do retículo endoplasmático, a Dissulfeto Isomerase Protéica (PDI). Contudo, tanto a relevância fisiológica como os mecanismos desta interação ainda não estão claros. O objetivo geral do presente trabalho é investigar por meio de experimentos de perda e ganho de função da PDI, a importância da PDI na migração celular associada à ativação do complexo NADPH oxidase, bem como possíveis mecanismos envolvidos na interação entre a PDI e esse complexo enzimático durante a migração celular. Os objetivos específicos são: i) avaliar o efeito do silenciamento da PDI, bem como da expressão forçada de PDI wild type na migração de VSMC in vitro; ii) analisar o efeito da transfecção de siRNA da PDI atividade e expressão de distintas isoformas da NADPH oxidase vascular e produção de ROS induzida por PDGF; iii) investigar o envolvimento de RhoGTPases na regulação do complexo NADPH oxidase pela PDI. No presente trabalho, mostramos que o PDGF induz redistribuição da PDI e aumento da produção de ROS. O silenciamento da PDI inibe a produção de ROS e a expressão do mRNA da Nox1, sem alterar a expressão do mRNA da Nox4. Mais ainda, o silenciamento da PDI reduz a migração celular induzida por PDGF, em diferentes modelos de migração, enquanto a super-expressão da PDI induz aumento espontâneo da migração na condição basal. Análise utilizando métodos de Biologia de Sistemas de redes de interação física proteína-proteína em bancos de dados e técnicas de análise de centralidade, topologia e ontologia gênica indicou forte convergência entre PDI e proteínas da família das pequenas RhoGTPases e seus reguladores. Em VSMC com silenciamento da PDI, a presença do PDGF induziu uma redução na atividade de Rac1 e RhoA, sem alterar a expressão total destas proteínas. Estudos mostraram que a PDI colocaliza com Rac1 na região perinuclear e co-imunoprecipita com Rac1 e RhoA, tanto na presença como na ausência de PDGF. Além disso, ocorreu a interação entre PDI e o regulador de GTPases RhoGDI (inibidor da dissociação da guanina) na condição basal (por microscopia confocal e co-imunoprecipitação), diminuída após estimulo com PDGF. O silenciamento da PDI induziu ainda alterações em estrutura de citoesqueleto: desorganização das fibras de estresse, e redução no número e tamanho de adesões focais e vesículas de adesão marcadas por RhoGDI e Rac1. Assim, os dados apresentados no presente trabalho sugerem que a PDI sustenta a migração de VSMC dependente de sinalização redox e RhoGTPases. Além disso, RhoGTPases podem ser um alvo proximal importante mediando a convergência entre PDI e o complexo NADPH oxidase / Vascular Smooth Muscle Cell (VSMC) migration into vessel neointima is a therapeutic target for atherosclerosis and post-injury restenosis. NADPH oxidase-derived oxidants synergize with growth factors to support VSMC migration. We described interaction between NADPH oxidases and the endoplasmic reticulum redox chaperone Protein Disulfide Isomerase (PDI) in many cell types. However, physiological implications as well as mechanisms of such association are yet unclear. The aim of the present work was to investigate, througth experiments of gain or loss of PDI function, the importance of PDI in VSMC migration associated to NADPH oxidase. The specific aims were: i) to evaluate effects of PDI silencing or PDI overexpression in VSMC migration in vitro; ii) to evaluate effects of PDI silencing on PDGF-induced NADPH oxidase isoform expression and ROS production; iii) to evaluate the involvement of RhoGTPases on NADPH oxidase regulation by PDI. We show here that PDGF promoted subcellular redistribution of PDI concomitant to ROS production and that siRNA-mediated PDI silencing inhibited such ROS production, while near-totally suppressing the increase in Nox1 expression, with no change in Nox4. Furthermore, PDI silencing inhibited PDGF-induced VSMC migration assessed by distinct methods, while PDI overexpression increased spontaneous basal VSMC migration. To address possible mechanisms of PDI effects, we searched for PDI interactome by PPPI networks, which indicated convergence with small GTPases and their regulator RhoGDI. PDI silencing decreased PDGF-induced Rac1 and RhoA activities, without change in their expression. PDI displayed small detectable points of perinuclear co-localization with Rac1 and co-immunoprecipitated with Rac1 and RhoA in a PDGF-independent way. Moreover, there was PDI association with RhoGDI at baseline (confocal and co-immunoprecipitation), decreased after PDGF. Of note, PDI silencing promoted strong cytoskeletal changes: branched stress fiber disorganization, markedly decreased number of focal adhesions and reduced number of RhoGDI-containing vesicular recycling adhesion structures. Overall, these data suggest that PDI is required to support redox and GTPase-dependent VSMC migration. Moreover, RhoGTPases are a potential upstream target mediating the convergence between PDI and NADPH oxidase

A inibição do transporte axonal é um evento que ocorre prematuramente no curso das doenças neurodegenerativas, inclusive antes da formação dos agregados proteicos, os quais estariam envolvidos no processo fisiopatológico das doenças neurodegenerativas. No presente estudo avaliou-se a hipótese de que alterações no transporte de mitocôndrias ocorrem antes da formação dos agregados proteicos envolvidos em neurodegeneração, devido a desregulação dos níveis citoplasmáticos de Ca2+ e o envolvimento da modulação do transporte mitocondrial provido pela proteína Miro neste cenário. Utilizaram-se dois modelos experimentais: o primeiro utilizando a exposição à rotenona em culturas primárias de neurônios do locus coeruleus, hipocampo e substância negra de ratos, e o segundo utilizando neurônios derivados de células tronco de pluripotência induzida (iPSC), isogênicas humanas contendo mutações que levam à deleção do exon 9 da (deltaE9) no gene da presenilina 1 (PS1), o qual apresenta aumento da síntese do peptídeo beta-amiloide com 42 aminoácidos (Abeta42), sem a formação de agregados proteicos. Os resultados mostram disfunções nos níveis citoplasmáticos de Ca2+ em ambos modelos. A mobilidade mitocondrial alterou-se no hipocampo, locus coeruleus e substância negra após exposição à rotenona. No entanto, a direção das alterações observadas não se correlacionaram com os níveis de Ca2+, de acordo com o já descrito na literatura. Não houve alteração da mobilidade mitocondrial, nem nos níveis de Miro1, nos neurônios derivados de iPSC. Em conclusão, o presente estudo demonstrou que alterações nos níveis citoplasmáticos de Ca2+ ocorrem antes e durante a formação de agregados proteicos, o que pode ser importante para a etiologia de doenças neurodegenerativas. Foi também demonstrado que mudanças na mobilidade mitocondrial, acompanhadas por alterações nas concentrações intracelulares de Ca2+, em níveis fisiológicos, ocorrem de forma independente dos níveis da proteína Miro1 em culturas de células. Porém são necessários novos estudos a fim de relacionar alterações na mobilidade mitocondrial e a indução da neurodegeneração / The axonal transport impairment occurs early in neurodegenerative diseases, even before the formation of protein aggregates, which are related with the neuropathophysiology mechanism in neurodegenerative diseases. In this study, we evaluate the hypothesis that disruptions in mitochondria transport occurs before the formation of protein aggregate related with neurodegeneration, triggered by dysregulations in cytosolic Ca2+ levels and the involvement of Miro Ca2+ dependent mechanism of mitochondria trafficking modulation. We employed two experimental models, first using rotenone exposure in primary neuronal cell cultures from locus coeruleus, substantia nigra and hippocampus of newborn rats. Second, using isogenic human neurons derived from induced pluripotent stem cells (iPSCs), harboring mutations, those induce exon 9 deletion (deltaE9) in Presenilin 1 (PS1) gene, and showing increased synthesis of amyloid beta peptide with 42 amino acids (betaA42) without the formation of protein aggregates. We found abnormalities in cytosolic Ca2+ levels in both experimental models, mitochondria trafficking were altered in hippocampus, substantia nigra and locus coeruleus. However, the pattern of mitochondria trafficking alterations did not correlate with cytosolic Ca2+ levels, accordingly with the data that was already published. We did not find alterations in mitochondria trafficking or Miro1 levels in neurons derived from iPSC. In conclusion, our finds demonstrated aberrant cytosolic Ca2+ levels before and during protein aggregation, which may be important for the etiology of neurodegenerative diseases. In addition, this dysfunction in mitochondria trafficking happens after changes in cytosolic Ca2+ levels, in physiological range, independent of Miro1 levels in primary neurons cell cultures. Therefore, new studies need to be done, aiming to elucidate the relation between mitochondria trafficking dysfunctions and the induction of neurodegeneration process.

A inibição do transporte axonal é um evento que ocorre prematuramente no curso das doenças neurodegenerativas, inclusive antes da formação dos agregados proteicos, os quais estariam envolvidos no processo fisiopatológico das doenças neurodegenerativas. No presente estudo avaliou-se a hipótese de que alterações no transporte de mitocôndrias ocorrem antes da formação dos agregados proteicos envolvidos em neurodegeneração, devido a desregulação dos níveis citoplasmáticos de Ca2+ e o envolvimento da modulação do transporte mitocondrial provido pela proteína Miro neste cenário. Utilizaram-se dois modelos experimentais: o primeiro utilizando a exposição à rotenona em culturas primárias de neurônios do locus coeruleus, hipocampo e substância negra de ratos, e o segundo utilizando neurônios derivados de células tronco de pluripotência induzida (iPSC), isogênicas humanas contendo mutações que levam à deleção do exon 9 da (deltaE9) no gene da presenilina 1 (PS1), o qual apresenta aumento da síntese do peptídeo beta-amiloide com 42 aminoácidos (Abeta42), sem a formação de agregados proteicos. Os resultados mostram disfunções nos níveis citoplasmáticos de Ca2+ em ambos modelos. A mobilidade mitocondrial alterou-se no hipocampo, locus coeruleus e substância negra após exposição à rotenona. No entanto, a direção das alterações observadas não se correlacionaram com os níveis de Ca2+, de acordo com o já descrito na literatura. Não houve alteração da mobilidade mitocondrial, nem nos níveis de Miro1, nos neurônios derivados de iPSC. Em conclusão, o presente estudo demonstrou que alterações nos níveis citoplasmáticos de Ca2+ ocorrem antes e durante a formação de agregados proteicos, o que pode ser importante para a etiologia de doenças neurodegenerativas. Foi também demonstrado que mudanças na mobilidade mitocondrial, acompanhadas por alterações nas concentrações intracelulares de Ca2+, em níveis fisiológicos, ocorrem de forma independente dos níveis da proteína Miro1 em culturas de células. Porém são necessários novos estudos a fim de relacionar alterações na mobilidade mitocondrial e a indução da neurodegeneração / The axonal transport impairment occurs early in neurodegenerative diseases, even before the formation of protein aggregates, which are related with the neuropathophysiology mechanism in neurodegenerative diseases. In this study, we evaluate the hypothesis that disruptions in mitochondria transport occurs before the formation of protein aggregate related with neurodegeneration, triggered by dysregulations in cytosolic Ca2+ levels and the involvement of Miro Ca2+ dependent mechanism of mitochondria trafficking modulation. We employed two experimental models, first using rotenone exposure in primary neuronal cell cultures from locus coeruleus, substantia nigra and hippocampus of newborn rats. Second, using isogenic human neurons derived from induced pluripotent stem cells (iPSCs), harboring mutations, those induce exon 9 deletion (deltaE9) in Presenilin 1 (PS1) gene, and showing increased synthesis of amyloid beta peptide with 42 amino acids (betaA42) without the formation of protein aggregates. We found abnormalities in cytosolic Ca2+ levels in both experimental models, mitochondria trafficking were altered in hippocampus, substantia nigra and locus coeruleus. However, the pattern of mitochondria trafficking alterations did not correlate with cytosolic Ca2+ levels, accordingly with the data that was already published. We did not find alterations in mitochondria trafficking or Miro1 levels in neurons derived from iPSC. In conclusion, our finds demonstrated aberrant cytosolic Ca2+ levels before and during protein aggregation, which may be important for the etiology of neurodegenerative diseases. In addition, this dysfunction in mitochondria trafficking happens after changes in cytosolic Ca2+ levels, in physiological range, independent of Miro1 levels in primary neurons cell cultures. Therefore, new studies need to be done, aiming to elucidate the relation between mitochondria trafficking dysfunctions and the induction of neurodegeneration process.

A migração de células musculares lisas (VSMC) da camada média do vaso para a íntima é essencial para vasculogênese e contribui para o processo de aterosclerose e estenose após lesão por cateter-balão, caracterizando-se como um importante alvo terapêutico. Diversos trabalhos já demonstraram que fatores de crescimento (como PDGF e FGF) estimulam a migração de VSMC, inclusive, muitos desses fatores de crescimento induzem sinalização redox associadas à geração de espécies reativas de oxigênio (ROS) (ex. Nox1 NADPH oxidase). Nosso grupo já descreveu interações físicas e regulação funcional da NADPH oxidase por uma chaperona redox do retículo endoplasmático, a Dissulfeto Isomerase Protéica (PDI). Contudo, tanto a relevância fisiológica como os mecanismos desta interação ainda não estão claros. O objetivo geral do presente trabalho é investigar por meio de experimentos de perda e ganho de função da PDI, a importância da PDI na migração celular associada à ativação do complexo NADPH oxidase, bem como possíveis mecanismos envolvidos na interação entre a PDI e esse complexo enzimático durante a migração celular. Os objetivos específicos são: i) avaliar o efeito do silenciamento da PDI, bem como da expressão forçada de PDI wild type na migração de VSMC in vitro; ii) analisar o efeito da transfecção de siRNA da PDI atividade e expressão de distintas isoformas da NADPH oxidase vascular e produção de ROS induzida por PDGF; iii) investigar o envolvimento de RhoGTPases na regulação do complexo NADPH oxidase pela PDI. No presente trabalho, mostramos que o PDGF induz redistribuição da PDI e aumento da produção de ROS. O silenciamento da PDI inibe a produção de ROS e a expressão do mRNA da Nox1, sem alterar a expressão do mRNA da Nox4. Mais ainda, o silenciamento da PDI reduz a migração celular induzida por PDGF, em diferentes modelos de migração, enquanto a super-expressão da PDI induz aumento espontâneo da migração na condição basal. Análise utilizando métodos de Biologia de Sistemas de redes de interação física proteína-proteína em bancos de dados e técnicas de análise de centralidade, topologia e ontologia gênica indicou forte convergência entre PDI e proteínas da família das pequenas RhoGTPases e seus reguladores. Em VSMC com silenciamento da PDI, a presença do PDGF induziu uma redução na atividade de Rac1 e RhoA, sem alterar a expressão total destas proteínas. Estudos mostraram que a PDI colocaliza com Rac1 na região perinuclear e co-imunoprecipita com Rac1 e RhoA, tanto na presença como na ausência de PDGF. Além disso, ocorreu a interação entre PDI e o regulador de GTPases RhoGDI (inibidor da dissociação da guanina) na condição basal (por microscopia confocal e co-imunoprecipitação), diminuída após estimulo com PDGF. O silenciamento da PDI induziu ainda alterações em estrutura de citoesqueleto: desorganização das fibras de estresse, e redução no número e tamanho de adesões focais e vesículas de adesão marcadas por RhoGDI e Rac1. Assim, os dados apresentados no presente trabalho sugerem que a PDI sustenta a migração de VSMC dependente de sinalização redox e RhoGTPases. Além disso, RhoGTPases podem ser um alvo proximal importante mediando a convergência entre PDI e o complexo NADPH oxidase / Vascular Smooth Muscle Cell (VSMC) migration into vessel neointima is a therapeutic target for atherosclerosis and post-injury restenosis. NADPH oxidase-derived oxidants synergize with growth factors to support VSMC migration. We described interaction between NADPH oxidases and the endoplasmic reticulum redox chaperone Protein Disulfide Isomerase (PDI) in many cell types. However, physiological implications as well as mechanisms of such association are yet unclear. The aim of the present work was to investigate, througth experiments of gain or loss of PDI function, the importance of PDI in VSMC migration associated to NADPH oxidase. The specific aims were: i) to evaluate effects of PDI silencing or PDI overexpression in VSMC migration in vitro; ii) to evaluate effects of PDI silencing on PDGF-induced NADPH oxidase isoform expression and ROS production; iii) to evaluate the involvement of RhoGTPases on NADPH oxidase regulation by PDI. We show here that PDGF promoted subcellular redistribution of PDI concomitant to ROS production and that siRNA-mediated PDI silencing inhibited such ROS production, while near-totally suppressing the increase in Nox1 expression, with no change in Nox4. Furthermore, PDI silencing inhibited PDGF-induced VSMC migration assessed by distinct methods, while PDI overexpression increased spontaneous basal VSMC migration. To address possible mechanisms of PDI effects, we searched for PDI interactome by PPPI networks, which indicated convergence with small GTPases and their regulator RhoGDI. PDI silencing decreased PDGF-induced Rac1 and RhoA activities, without change in their expression. PDI displayed small detectable points of perinuclear co-localization with Rac1 and co-immunoprecipitated with Rac1 and RhoA in a PDGF-independent way. Moreover, there was PDI association with RhoGDI at baseline (confocal and co-immunoprecipitation), decreased after PDGF. Of note, PDI silencing promoted strong cytoskeletal changes: branched stress fiber disorganization, markedly decreased number of focal adhesions and reduced number of RhoGDI-containing vesicular recycling adhesion structures. Overall, these data suggest that PDI is required to support redox and GTPase-dependent VSMC migration. Moreover, RhoGTPases are a potential upstream target mediating the convergence between PDI and NADPH oxidase